Self-leveling bright nickel plating bath and process



United States Patent 3,017,333 SELF-LEVELING BRIGHT NICKEL PLATING BATH AND PROCESS Virgil H. Waite, Vermilion, and Bernard P. Martin, Cleveland Heights, Ohio, assignors to The McGean Chemical Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Apr. 6, 1959, Ser. No. 804,100

26 Claims. (Cl. 204-49) This invention relates to the electroplating of nickel upon a basis metal for protective and decorative purposes; more especially it relates to a bath, and a process employing the bath, for electroplating nickel either as a bright or semi-bright deposit, wherein there is used a new and highly advantageous organic addition agent functioning to improve the leveling action of the bath.

As used herein, the term leveling refers to the ability of an electrodeposited plate to effect obliteration or substantial hiding of surface imperfections of macroscopic size in the basis metal on which the plate is deposited. Good leveling results in a smooth, continuous surface which does not duplicate the small irregularities and roughness of the original surface of the basis metal.

Good self-leveling ability is highly desirable in nickel plating baths because it substantially reduces the amount of surface preparation, and the care with which this must he done, before plating an article. It may also eliminate bufiing of an initial plated deposit prior to the deposit of a further, final plating, as of chromium for example, where in the past such buffing has frequently been necessary, even though the production of bright nickel plate has become everyday practice. The invention however is more particularly concerned with the elimination of much of the polishing and buffing of the surface of the basis metal itself which has conventionally been involved in order to obtain, in the final result, a bright mirrorlike finish on the article to be plated. Automobile bumpers, bumper guards, grills, ornamental trim and similar automotive hardware are perhaps the principal items of manufacture today wherein the invention currently finds its most useful application. The intricate shapes and contours of such items, as well as the enormous number of pieces produced, make the job of preparing the initial rough surface of the cast or stamped metal of which such articles are generally composed a most important factor from the cost standpoint. Such items must almost without exception be hand polished and buffed, since these operations can not be performed practically by automation processes at the present time.

Thus it may be stated generally that the primary objective of the invention is that of reducing the necessity for extensive mechanical preparation of the surfaces of the metal articles in order to obtain, finally, a bright, mirror-like finish on such articles. That objective is achieved in substantial part by the improvement upon the leveling properties of a nickel plating bath afforded by the invention, whereby it becomes possible to eliminate a substantial amount of the usual finishing operations without having polishing marks, such as the striations of a polishing belt, appear in the finished article.

It is a further object of the invention to reduce or substantially eliminate bufiing or final polishing of an article which has had an initial nickel plating applied thereto, prior to the application of a final plating, usually of chromium. By this means an appreciable enonomy of nickel can be realized, since it no longer becomes necessary to plate an extra amount of nickel on the article to allow for reduction in that deposit during final buffing operations.

It is a further object to provide a nickel plating bath, and a process employing the same, which in addition to possessing good leveling properties also results in nickel Patented Jan. 16, 1962 deposits of bright to semi-bright character and of good ductility.

Another objective is the provision of a nickel plating bath which is productive of good nickel deposits in spite of relatively wide variations in operating conditions which are bound to occur in commercial practice.

With the foregoing objects in view, as well as others which will become apparent as the description proceeds, the invention consists in the novel plating processes and bath compositions which will be described in certain illustrative examples hereinafter and will then be more particularly pointed out in the appended claims.

According to the invention there is employed as a leveling agent in a standard aqueous acid Watts bath certain organic compounds which, broadly stated, comprise five and six membered ring compounds having two hetero atoms, one of which is always nitrogen while the other is either sulfur or selenium. Use of such leveling agent by itself in a standard Watts bath offers notable improvements with regard to leveling and the production of bright to semibright deposits. However, in such a bath, rather rigid control of plating operations is required, and for most practical purposes use of such a bath is confined to work or pieces of rather simple shape because plating current densities, which are of course affected by the shape of an article, below certain minimum levels, are not productive of good deposits. In general, current densities of less than 30 amperes per square foot at conventional plating temperatures of 50 to 55 C. result in rather severe grooving or striation and discoloration of the nickel deposit when the novel leveling agents of the invention are employed as the only additive. Satisfactory results are obtainable, however, at current densities of 30 amperes per square foot and above under the conditions mentioned above.

It will be understood of course ,that in the plating of articles, such as the automotive hardware items mentioned, they are conventionally hung on brackets or hangers in a plating tank and, while care is taken to orient the articles with respect to the placement of the anodes in the plating bath to minimize the variance in current densities, certain points on the surfaces of the articles are of necessity at different distances from the anodes than are other points because of curvature or contouring of the article surfaces. Geo-metric shape of an article also has a very important bearing on current densities because of polarity effects, shielding, etc. These variations have a tendency to produce inadequate plating at some points, while burning occurs at others. It is highly important, therefore, that plating baths be employed which provide substantial tolerance for such variations in operating conditions without adverse effect upon the plated deposit.

Applicants have discovered that the operational range of the novel leveling additives can be substantially extended by other, supplemental bath additives. Five principal classes of additives, in combination with the novel leveling agents, have been found useful either alone or in conjunction with each other. These additional classes of additives include those com-monly referred to as primary and secondary brighteners, conventionally used today in bright nickel plating, certain nonionic surfactants, certain amino compounds and, lastly, certain other, rather miscellaneous, compounds which, although apparently chemically quite unrelated, nevertheless have a corrective influence on the low cathode current density fault of the novel leveling agents. Further, detailed description of these classes of additives will appear hereinafter.

Each of these compounds functions to a different degree to shift or extend the operating range so as to permit satisfactory use of lower cathode current densities in the plating bath at practical operating temperatures. For

example, the use of a primary brightener in addition to the leveling agent in a standard Watts bath lowers the limitation on suitable cathode current densities from the aforesaid minimum of around 30 to about 20 amperes per square foot. The further inclusion of a secondary brightener, although not appreciably altering the lower limit of operable cathode current density, has the effect of imparting full brilliance to the plate in those sections which, because of article shape or configuration, have a tendency otherwise to achieve only semi-brilliance. The use of a secondary brightener thus produces a final nickel deposit of more uniform lustre overall. The addition of a nonionic surfactant, or one of the effective amino compounds or, alternatively, one of the miscellaneous group of compounds mentioned will permit still lower cathode current densities, in the neighborhood of 10 amperes per square foot, to be employed.

Experience has shown that, within the general description given hereinabove of leveling agents useful in practioing the invention, the more effective compounds are the following.

(1) Thiazoline compounds:

(at) 2,4-diketo thiazolidine, and the 3 and/or 5 position substituted derivatives thereof (b) Z-imino, 4-keto th-iazolidine, and the 3 and/ or 5 position substituted derivatives (2) Selenazoline compounds:

(a) 2,4-diketo selenazolidine (b) 2-imino, 4-keto selenazolidine (3) Thiazine compounds:

(a) 2,4-diketo tetrahydro 1,3-thiazine, and 6 position substituted derivatives (b) 2imino-1,3 thiazine-4-one, and the 6 position substituted derivatives Preliminary investigations indicate that other related compounds may also be used successfully. These include the 3 and/or S substituted derivatives of the compounds in groups 2(a) and 2(b) above; the and 5, 6 substituted derivatives of the compounds in groups 3(a) and 3(b) above; also selenazine compounds corresponding to the thiazine compounds in group 3. It has been found desirable however to observe certain limitations regarding the degree and complexity of the substituted products, as the more highly substituted compounds appear not only to lose leveling power, but to result in brittleness of the deposit. structurally these compounds can be represented generally by the following formulae:

4 t a 5 3N 5 i 6 2 1 X 1 'X M M wherein M is either sulfur or or the imino group (:NH).

So far as now appears, substitutions in the 3, 5 or '6 positions or combinations thereof, in the respective parent compounds mentioned above should be limited to alkyl and substituted alkyl (including the alkene and alkyne) homologues preferably having not more than 4 carbon atoms but containing as many as 6 if properly modified by a substituent group to provide adequate solubility of the compound in the plating solution. The substitutions on the alkyl group may include halo, nitro, sulfo, amino, carboxy, hydroxy, aldehyde, keto and oxy (ether linkage) radicals. Other substitutions on the parent compound may include phenyl and loweralkyl substituted phenyl (e.g. benzyl) radicals, and the halo, nitro, sulfo, amino, carboxy, hydroxy, aldehyde, keto or oxy (ether linkage) derivatives thereof. The halo, nitro, sulfo, amino, carboxy, hydroxy, aldehyde, keto and oxy (ether linkage) radicals may also be attached directly to one of the ring atoms of the parent compound. A list of specific leveling agents which have been used and found to give excellent results is set forth in the accompanying Table I.

selenium and X is oxygen 3 and/or 5 or 3, 6

4 TABLEI Approx. Opt. Concentration, g./l.

Leveling Agent 2,4-diket0 thiazolidine 2,4-diketo 5,5*dimethyl thiazolidin 2,4-diketo 5-methy1 thiazolidine 2,4-diketo 3-propanone thiazolid 2,4-diket0 3-methyl tliiazolidihe 2,4-diketo 3-allyl thiazolidinm ZA-diketo 3,5-dimethyl thiazolidine- 2,4-dilreto 3-acetyl thiazolidine. 2,4-diketo 3-benzyl thiazolidine-.. 2,4-dilreto 3(n-butyl) thiazolidinm 2,4 diketo 5-acetic acid thiazolidine" 2,4-diketo 3-ethyl thiazolidine 2,4-dikcto B-phenyl thiazolidine- 2,4-diketo fi-(n-butyl) thiazolidine. 2,4-diketo 5-is0pr0pyl thiazolidine- 2,4-diketo 3-ethanol thiazolidine 2,4-diket0 5-ethyl thiazolidine ZA-diketo B-ethylamine thiazolidine s. 2,4-diketo 3-ethyl sulfonic acid thiazolidine 2,4-diketo B-acetamide thiazolidine ZA-diketo B-propionic acid thiazolidine 2,4-diketo 3-propi0nitrile thiazolidine 2,4-diketo 5-methyl acetate thiazolidine. 2,4diketo 5'acetamide thiazolidine 2,4-diketo 5-(3-methy1 4-hydroxy) benzylidine thiazolidine. 2,4-diket0 3-propio11ic acid 5-isopropyl thiazolidine.

2,4-diketo 3,5-diacetio acld thiazolidine 0 2,4-diketo 3-acetic acid 5-methyl thiazolidine. 0

2,4-diketo 3-acetic acid 5-butyl thiazolldine 10 ZA-dikcto 3-acetic acid thiazolidine 14 2,4-diketo S-ethanol 5-acetie acid thiazolidlne 10 2,4-diketo 5,5-dially1 thiazolidine 15 ZA-diketo 5-nitro thinzolidine. 07 2,4-diketo fi-sulionic acid thiazo t 10 2,4-diket0 5-allyl thiazolidine O3 2,4-diketo 5phenyl thiazolidine 08 2,4-diketo 5,5-diphenyl thiazoli l0 2,4-diketo 3-phenyl thiazolidine. 2,4-diketo 5-bromo thiazolidine... 0. 05 bgffliketo 3-amine hydrochloride thi 0.07

5,5-di(2-imino 4-keto) thiazolidine 0.05 2-iruin0 4-ket0 5-brornomethyl thiazohdine- 0.05

2-imino phenyl 4-keto 3-phenyl thiazolidine- Z-imino 4-keto thiazolidine Z-lmino 4-keto 3-isopropyl alcohol thiazolidine. 2-imino 4-keto B-acetyl thiazolidine t- Z-imino 4-ket0 S-ethyl thiazolidine 2-imin0 4-keto 3-formamide thiazolidine 2,4-diket0 1,3-thiazine 2,4-diketo ti-carboxy 1,3-thiazine 2,4-diketo fi-phenyl 1,3-thiazine. t. 2,4-diketo fi-benzaldehyde l,3-thiazine. 2,4-diketo (Ho-chlorophenyl) 1,3-thiazine 2,4-diketo G-(m-nitrophenyl) 1,3-thiazine- Z-imino 4-ket0 Mm-nitrophenyl) 1,3-thiazine. 2,4-diketo selenazolidine 2-imino t-keto selenazolidine 999999999999 99 o 0001 103 men The amount of leveling agent to be added to the bath Varies of course with the particular agent, as well as with certain other factors such as the presence of one or more other additives from the classes mentioned, and the plating temperature. In general, however, significant improvement both in leveling, as well as in brightening effect, begins to appear with the addition of 0.01 gram of the agent per liter of solution. The upper limit of leveling agent addition is generally substantially less than one gram per liter of solution, and optimum results are usually obtained within the range of about 0.02 to 0.08 gram per liter. Some of the compounds which are of the more highly substituted types require slightly greater concentrations to be employed in the plating bath in order to develop optimum leveling and brightening properties. As will be pointed out in greater detail hereinafter, concentrations of some of these latter leveling compounds vary from about 0.1 to 0.5 gram per liter for best results.

The use of a primary brightener in conjunction with the leveling agent has been found most helpful in easing the need for rigid, close control of the plating process. The addition of a compound such as naphthalene 1,6-disulfonic acid, for example, is quite elfective. Other diand tri-naphthalene sulfonics, and the group of agents commonly known today to be useful as primary addition agents in bright nickel plating baths may likewise be employed. Such other agents include naphthol sulfonic acids, naphthylamine sulfonic acids, toluidine sulfonic acids and tolidine sulfonic acids. Mildly chlorinated forms of these agents are also suitable. Aryl sulfonamides, aryl sulfimides and substitution products thereof are other suitable primary brighteners, of which orthobenzoic sulfirnide, benzene sulfonamide, benzene sulfohydroxamic acid and ortho and para-toluene sulfonamides are representative. These are disclosed in the prior patents of V. H. Waite, Nos. 2,112,818 and 2,114,006, and of Lind et al. No. 2,198,268. These primary brighteners may be employed in their usual concentrations in bright nickel plating baths, ranging from approximately 0.5 to 25 grams per liter of bath solution. Normally optimum results are obtained at concentrations of 0.5 to 5.0 grams per liter.

Secondary brighteners of known type for bright nickel plating baths can likewise be used to advantage with the primary brightener and the leveling agent. As previous ly mentioned, the function of the secondary brightener is primarily that of obtaining a deposit of more uniform brilliance, thereby reducing the necessity for bufling of the initially plated item prior to the deposit of a final, e.g. chromium, plate. Among the secondary addition agents found useful are the amino poly aryl methane compounds including fuchsin, reduced fuchsin, p,p'-methylene dianiline and 2,2',4,4-tetramino-5 ,5 '-dimethyl dipheny-lmethane. Other secondary brighteners of this general type are disclosed in the patent to Lind et al. mentioned above. Satisfactory concentrations of these secondary brighteners should be at least 2 milligrams per liter of bath solution and may range up to as high as 100 milligrams although about 20 milligrams is the preferred upper limit.

As previously mentioned, several additional families or groups of organic compounds have been discovered by the present inventors which do not belong in the conventional primary or secondary agent categories of compounds used in bright nickel plating, yet they have a rather remarkable elfect in extending the low cathode current density range of sound deposits to a lower value in a standard Watts bath incorporating one of the novel leveling agents than is obtained by employing with the leveling agent only a conventional primary brightener, such as naphthalene disulfonic acid, for example. These groups of compounds, which are herein termed generally as extenders, comprise the three remaining bath additives of the five types mentioned hereinbefore. Normally, only one of these extenders is used at any one time in a given plating bath. A compound from one of these families or groups is able, for example, to lower the practical current density operating range of a bath containing one of the novel leveling additions to at least as low as amperes per square foot at the plating temperature and bath acidity conditions conventionally encountered in bright nickel plating.

Compounds in the first group of these extenders are referred to herein as nonionic surfactants. Of the three groups of extenders mentioned, these appear presently to be the most important. Not all nonionic surfactants are satisfactory, however, and effective results are limited to those members of this family having higher molecular weights. Other factors influencing the suitability of these nonionics are the minimum cloud point and the existence of incomplete nonionicism. Compounds in this group include those having a molecular weight of around 7,000 or more resulting from the reaction of polypropylene glycol and ethylene oxide; propylene and ethylene oxides with ethylenediamine; and fatty acids, such as stearic, with alkylene oxides. Representative commercially available compounds include the following:

(a) Pluronic F68, the trade name of Wyandotte Chemicals Corporation of Wyandotte, Mich, for a reaction product of propylene glycol and ethylene oxide, the simplified general formula for which may be represented as HO(C H,O) (C l-I O) ,(C I-L O) H, having a molecular weight of approximately 6800 to 8975, and being sold commercially in the form of the free-flowing white flakes having a melting point in excess of 50 C., and being freely soluble in water, its cloud point being in excess of C.

(b) Tetronic 908, also a product of Wyandotte, which results from sequential addition of propylene and ethylene oxides to ethylenediamine, the simplified general and the molecular Weight of which is about 27,000, being sold commercially in flake form and having a melting point of about 58 C., also freely soluble in water up to the boiling point.

(c) Tergitol XC and Tergitol XD which are trade names of Carbide and Carbon Chemicals Company for high molecular weight polyalkylene glycol ethers sold in white soft-solid form, completely soluble in water up to boiling.

(d) MYRI 53, a product of Atlas Powder Company, comprising a high molecular weight reaction product of a fatty acid and an alkylene oxide, sold as a Waxy solid which is completely soluble in water up to boiling.

As to the desired amount of such extenders in a plating solution, this of course varies with the particular extender employed but in general it ranges from at least 0.005 to about 0.1 g./l. of solution, and generally the maximum is on the order of 0.05 g./ 1., as higher concentrations appear to impair the leveling property ofthe leveling agent to some extent and to produce some brittleness in the deposit.

It has also been found important when one of the foregoing nonionic surfactants is used in a bath which also contains an anionic compound, such as sodium lauryl sulfate for purposes of preventing pitting in the electro-deposited nickel plate, that the nonionic surfacant should either be added to the 'antipitter before the two are introduced into the plating bath, or that the nonionic compound should be added to the bath after the anionic compound. Both of these procedures have been shown to ensure consistently satisfactory plating results, whereas adding the nonionic compound before addition of the other may cause difficulty.

A second type of extender found to provide similarly useful effect upon baths containing one of the novel leveling agents, either alone or in combination with a primary, or a primary and secondary brightener, are compounds possessing amino groups. Here again, all amino compounds are not necessarily eifective, those having been found particularly suitable include ethylene-diamine tetraacetonitrile, adenine sulfate, tetraethylene pentamine and methyl violet. Suitable amounts of these compounds in solution range from 0.01 to less than 0.1 gram per liter, with a preference for the lower concentrations again, in order to avoid brittleness of the deposit and impairment of the leveling action.

Still other compounds which appear to be completely unrelated to each other have also been found useful, and these make up the third group of extenders mentioned above. Among this latter group are nucleic acid, ter'ephthalonitrile and Carbowax 20-M, the trade name of Carbide and Carbon Chemicals Co. for a waxy, solid polyethylene glycol product having a molecular weight of around 15,000 to 20,000. Concentrations of 0.01 to 0.05 gram per liter for the first and second compounds just mentioned, and a somewhat lesser amount, e.g. from 0.01 to 0.025 g./l. for the Carbowax 20-M, when used in combination with diketo thiazolidine as a leveling agent, have proved effective. Higher concentrations of the respective extender compounds in this group again show a tendency to cause brittleness and to have other undesirable effects on the plated deposit.

Specific examples of plating solutions employing these 7 extenders and suitable operating conditions, are presented hereinafter.

In general, the process of the invention involves operating a bath at conventional bright nickel plating temperatures ranging from about 30 C. to as high as 80 C. with a range of 50 to 55 C. being especially desirable. The pH of the plating baths, as determined electrochemically, may range from around 5.0 to a minimum of 2.5, with 3.0 to 2.5 being found especially suitable in the majority of cases. The Watts bath solution to which the leveling agent is added typically comprises around 300 g./l. of nickel sulfate, 60 g./l. of nickel chloride and 4-5 g./l. of boric acid. The foregoing bath composition and specified operating conditions are not critical in that the basic Watts bath solution and the particular temperature and pH thereof may vary within the indicated ranges without adverse effect. Considerable latitude is also permissible in respect to the types and concentrations of the nickel salts employed in the basic Watts bath.

In order to illustrate further the principles of the invention, detailed examples demonstrating typically good practice in applying the teachings of this disclosure will now be given.

Example 1 A nickel plating bath composition employed for this and subsequent examples was prepared containing, per liter of solution, approximately 300 grams of nickel sulfate, 60 grams of nickel chloride and 45 grams of boric acid. To this, 0.12 gram of sodium lauryl sulfate was added as an antipitting agent. This solution forms the basis for all plating tests described in the various illustrations given in these examples, being supplemented by the addition of various leveling agents, primary and sec ondary brighteners and extenders as described in the respective cases. In this first example, 2,4-diketo thiazolidine was added, and nickel plate deposits of a uniform thickness of 0.001 inch were made at a constant cathode current density of 50 amps/sq. ft. using different amounts of the leveling additive in each test. In order to provide a basis for effective comparison of the leveling effect, the nickel deposits were plated over test strips of ordinary soft steel having specially prepared abraded areas of predetermined, uniform depth on one surface. The leveling effect can thus be determined by visual inspection to note the degree of obliteration of the surface irregularities in the abraded areas produced by the plated deposits under the different conditions. The temperature of the bath during the plating operation was 55 C. and the pH was 3.0.

Substantial improvement both in brightening effect as well as leveling was obtained under the above conditions at concentrations of 0.01, 0.02, 0.04, 0.06, 0.08 and 0.10 g./l. of the leveling agent. The optimum range is from slightly below 0.01 to 0.04 g./l., with best results obtained at around 0.02 g./1.

The above bath composition and operating conditions are not critical and can be varied over relatively wide ranges for the most part, provided the amount of leveling agent is properly controlled. However, for best result, the pH should be no lower than 2.5 and the cathode current density should be at least 30 amps/sq. ft. or above in the described bath. At lower current densities this bath exhibits a tendency to produce grooving in the plated deposit, and at a current density of around 20 amps/sq. ft. the grooving becomes quite pronounced, even at the optimum leveling agent concentration of 0.02 to 0.04 g./l. Accordingly such a bath generally requires modification by employment of extenders to be fully practical in most instances. The use of extenders as well as additional brighteners in this bath will be described in greater detail presently.

Example 2 This example serves to illustrate the effectiveness of the parent thiazolidine compound substituted in the 5 position. Employing the same basic or initial plating solution as in Example 1, but using 2,4-diketo S-methyl thiazolidine as the leveling agent in this case, substantial improvement in brightness and leveling are again obtained at concentrations of from 0.01 to around 0.06 g./l. of the leveling agent, with an optimum at approximately 0.05 g./l. under the operating conditions above specified.

Example 3 In order to show the effectiveness of the parent thiazolidine agent substituted in the 3 position, in this example all conditions are again the same as in Example 1 except that the leveling agent employed is 2,4-diketo-3-methyl thiazolidine. The operative range of concentrations in this instance is from approximately 0.01 to somewhat above 0.05 g./l., with optimum results obtained at about 0.04 g./l.

Example 4 Again the standard bath and operating conditions specified in Example 1 obtain, but the leveling agent employed here is 2,4-diketo S-methyl 3-methyl thiazolidine. Substantial improvement in leveling, as well as brightness, of the plated deposit is noted at concentrations of this leveling agent ranging from about 0.01 to around 0.06 g./l. This illustrates the effectiveness of the parent diketo thiazolidine agent substituted in both the 3 and 5 positions.

As has been mentioned, the parent diketo thiazolidine and its substituted derivatives are effective to give deposits with excellent leveling, excellent ductility and fine grain under conditions where the cathode current density is maintained above 30 amps./ sq. ft., and for this reason these compounds used alone in the standard plating bath impose limitations in practical operation, so that only relatively simple work, that is work of generally planar configuration, can be readily handled. The inventors have found that improvement in this respect can be obtained by the addition of a primary brightener of known composition, such as naphthalene disulfonic acid, along with the leveling agent, in the standard Watts bath. Such improvement is illustrated by the following example.

Example 5 A bath prepared in accordance with Example 1, but containing in addition as little as 6 gallons/ 1000 of bath solution of naphthalene 1,6-disulfonic acid (equivalent to about 1.0 g./l.) gives materially improved results at the leveling agent concentrations specified in Example 1 and at cathode current densities below 30 amps/sq. ft. Even at 20 amps/sq. ft. a semi-bright, level, ductile deposit is obtained which is free of the grooving which is noted at such low cathode current densities in the absence of the naphthalene disulfonic acid. Tests further show that other agents in the conventional primary brightener category, such as naphthalene trisulfonic acid and others referred to hereinbefore in a general discussion of these primary brighteners, produce similar results. A further elfect is noted here also, in that the presence of the leveling agent definitely enhances or supplements the brightening effect of the primary brightener used alone.

Still further improvement is obtained by the inclusion of a secondary brightener, along with a primary brightener and leveling agent, in the standard bath. While the secondary brightener, for example reduced fuchsin, does not extend the sound nickel deposition to cathode current densities substantially below 30 amps/sq. it, it does result in imparting full brilliance to the semi-bright sections of the nickel deposit otherwise obtained, resulting in a final nickel deposit of over-all uniform luster.

However, the tolerance of the novel plating solutions to variation of cathode current density, particularly at the lower values, is very substantially improved by the employment of one of the organic extender compounds mentioned hereinabove. This is illustrated by the following examples.

Example 6 The plating solution employed in this example is basically the same as that described in Example 5, with the further addition of a nonionic surfactant Pluronic F68 as described hereinabove, the concentration of the leveling agent (2,4-diketo thiazolidine) being maintained constant at 0.05 g./l. in this case. Plated deposits made at the standard plating temperature and pH specified in Example 1 at various concentrations of the surfactant demonstrate that full bright, ductile, fine grained nickel deposits are obtained at cathode current densities of at least as low as amps/sq. ft. in the range of from about 0.02 to around 0.07 g./l. of the surfactant. At the lower end of this range, some grooving and some blackening of the plated deposit is noted, while at the higher end of the specified range, the ductility of the plate oegins to drop off. The very best results are obtained under the stated conditions with a concentration of about 0.03 g./l. of the specified surfactant.

Example 7 A plating solution similar to that described in the immediately foregoing example but employing as the nonionic surfactant extender a compound sold under the trade name Tergitol-XC in concentrations of from around 0.02 to 0.05 g./l. produces equally good results. The optimum concentration of the surfactant in this case is around 0.025 g./l. Again, concentrations lower than those just mentioned show grooving of the plated deposit at cathode current densities of as little as 10 amps./ sq. ft., while brittleness of the deposit beings to appear at concentrations of the surfactant above the indicated range.

Example 8 The same bath composition as described in Example 6 is again employed, but in this case the nonionic surfactant extender employed is Tergitol-XD. The operable range of concentration for this material is substantially narrower than that in the preceding example, being on the order of 0.03 to 0.04 g./l. in this instance if grooving or impairment of ductility of the deposit is to be avoided.

Example 9 Again the bath composition is the same as in Example 6, except that the surfactant employed is Tetronic 908. The operable range of concentration here runs from below 0.04 g./l. to as high as 0.08 g./l., at a cathode current density of 20 amps/sq. ft., as impairment of the ductility of the plated deposit does not become appreciable until concentrations of around 0.09 to 0.10 g./l. are employed. All deposits Within the indicated operating range are of full brightness and free of any grooving, although the optimum concentration lies in the range of approximately 0.04 to 0.06 g./l.

Example 10 current densities, and the following group of examples illustrates the effectiveness of those extenders which are referred to hereinabove as the amino compounds. Although the amino compounds are not as marked in their improvement as are the nonionic surfactant materials illustrated in the foregoing set of examples, they nevertheless are capable of permitting practical operating conditions at the lower cathode current densities commonly encountered in practice. The use in the bath solution of a primary brightener of the described type seems in this case to be desirable if not essential for effectiveness of the amino compounds, however.

Example 11 Nickel deposits of uniform thickness produced in a bath containing ethylenediamine tetraacetonitrile instead of the nonionic surfactants, in baths otherwise the same as those in Examples 6 through 10 hereinabove, show satisfactory brilliance and ductility at cathode current densities of 20' amps/sq. ft. when the concentration of the extender compound in this instance ranges from slightly below 0.01 g./l. to around 0.02 g./l. At 0.01 g./l. of the amino compound, the plated deposit is of substantially full brilliance and is ductile. Ductility, however, drops oif sharply at increased concentrations of the extender.

Example 12 The extender employed in this instance is adenine sulfate in a plating bath otherwise the same as that used in the preceding examples. Operable concentrations of this extender min from approximately 0.01 to 0.05 g./l., at 20 amps./sq. ft., semi-brightness being developed at the lower concentrations with full ductility, while full brightness of the plate is developed at the higher end of the concentration range but with a concomitant reduction in ductility.

Example 13 The conditions in this test are the same as those in the immediately preceding example except that the extender employed is tetraethylene pentamine. The operable range of concentrations of the extender here is from somewhat below 0.005 g./l. to 0.04 g./l. Best results are obtained in the range of 0.005 to 0.01 g./l., wherein deposits of full brilliance and full ductility result.

Example 14 Again the conditions of plating and bath composition are the same as those just described except that the extender employed is methyl violet. Semi-bright, fully ductile deposits at 20 amps./ ft. sq. are obtained at a concentration of 0.025 g./l., and the operable range of concentration of the extender in this case runs to somewhat over 0.10 g./l. Full brilliance and full ductility are retained at a concentration of 0.10 g./l., and ductility as maintained through a concentration as great as 0.20 g./l., but at this latter concentration the plated deposit takes on a grayish matte appearance. No grooving, however, appears anywhere within the concentration range specified.

Certain miscellaneous extenders referred to herein- ;before likewise serve to improve the tolerance of the plating baths containing the novel leveling agents in respect to variation in cathode current density. Illustrations of three such compounds will be given.

Example 15 The bath composition employed here is the same, with the exception of the extender material, as that described in the immediately foregoing example. In this case the extender used is nucleic acid, and operable concentrations of this compound range from somewhat below 0.04 g./1. to slightly above 0.08 g./l. when plating at cathode current densities as low as 20 amps./ sq. ft. Semi-brilliance and good ductility are obtained at 0.04 g./l.; improved brilliance and full ductility at 0.05 g./ 1.; and full brilliance at 0.08 g./l., but at reduced ductility.

Example 16 The extender employed in this case is Carbowax 20-M in a plating solution otherwise the same as the foregoing example. Good results are obtained at concentrations of this extender ranging from around 0.025 g./l. to 0.10 g./l., all of which concentrations produce deposits which are fully ductile. At the lower end of the range, the deposit is semi-brilliant, while full brilliance appears at about the midpoint of the range specified. Brilliance again deteriorates at concentrations above 0.1 g./l., but in this case the ductility is fully maintained, even at concentrations as high as 0.2 g./l. These results obtain at the low current density conditions of 20 amps./ sq. ft., as before.

Example 17 The extender employed here is terephthalonitrile in a plating solution and under conditions otherwise identical with those described above. Freedom from grooving at cathode current densities as low as 20 amps/sq. ft. is again obtained at concentrations of the extender ranging from about 0.01 to 0.10 g./l. The deposits are fully ductile within the range of 0.01 to 0.05 g./l. and full brilliance is developed at a concentration of around 0025 g./l. in this instance.

It has been observed generally that in addition to the limitation on the use of higher concentrations of any of the extenders imposed by the reduction in brilliance and ductility of the resulting deposit, there is a tendency of the extenders to impair the leveling action of the novel leveling agents. It is accordingly desirable that the concentration of the extender be kept to a minimum where it is still eifective to correct the low cathode current density fault of the particular bath in which it is used. This is more especially true of the amino compounds and those which have been classified as comprising the miscellaneous group.

The foregoing examples have each employed diketo thiazolidine or one of its aklyl substituted derivatives as the leveling agent. It is to be understood, however, that these examples are merely illustrative of the results obtained when using any of the thiazolidine compounds coming within the general description of this class of compounds, including the imino derivatives as well as halo, nitro, sulfo, amino, carboxy, hydroxy, aldehyde and oxy (either linkage) and benzyl and phenyl substituted products discussed previously and included in Table I. The foregoing also applies to the employment of leveling agents from the other classes, other than the thiazolidines, which have been mentioned hereinbefore. The following examples are illustrative of this.

Example 18 A standard Watts bath prepared as in Example 1 has incorporated in it a suitable amount of a primary brightener, such as naphthalene 1,6-disulfo-nic acid, and 2,4- diketo selenazolidine as a leveling agent. Good leveling and semi-bright deposit result at concentrations of 0.01 to 0.02 g./l. of the selenazine compound at a plating current of 50 amps./ sq. ft. The leveling effect of this agent drops off materially at a concentration of around 0.03 to 0.04 g./l., but picks up again at concentrations of 0.06 to 0.2 g./l. Some grooving, however, appears at around 0.06 to 0.07 g./l. but disappears completely at higher concentrations although the ductility is reduced at such higher concentrations. The low cathode current density tolerance can be increased here again by the incorporation of one of the extenders.

Example 19 In this case, the leveling agent employed in a bath otherwise identical with that in the preceding example is 2,4-diketo tetrahydro 1,3-thiazine. At a plating current of 50 amps/sq. ft., excellent leveling is obtained at concentrations of the thiazine compound ranging from around 0.01 to 0.10 g./l., with optimum results appearing at about 0.05 g./l. Throughout this range the deposits are ductile and run from a dull or mat finish at the lower end of the range to a full bright appearance at the upper limits specified. The use of extenders here also Widens the practical operating limits of the bath in respect to its tolerance for low cathode current densities.

The use of the thiazolidine, thiazine, selenazolidine and selenazine compounds hereinabove specifically named, as leveling agents in nickel plating baths, is believed to be broadly novel irrespective of the quantity or concentrations thereof in such baths or of other operating conditions under which such baths are employed. It is further believed that the combined use of one of these leveling agents with a primary, or with primary and secondary brighteners of the type mentioned, and particularly with the addition of an extender of the kind described hereinabove, is likewise broadly novel in the nickel plating art to which this invention specifically pertains.

While the specific examples above have each employed naphthalene 1,6-disulfonic acid as the primary brightener, similar results are obtained with other primary brighteners within the groups of such compounds which are discussed hereinabove. Some of these which have shown satisfactory results include benzene disulfonic acid, saccharin, benzene sulfonarnide, toluene sulfonamide and ortho-sulfobenzoic anhydride, but since the conditions of bath composition and operating limits are otherwise substantially identical with the examples given, further examples specifically employing these primary brighteners need not be included here.

The foregoing generalization applies also to the'use of secondary brighteners other than reduced fuchsin. The use of such other secondary brighteners within the broad definition given hereinabove of this class of additives should accordingly be understood as contemplated by the invention.

Therefore, although the invention has been illustrated by the various specific examples given hereinabove, it will be appreciated that these are simply illustrative and that the invention is capable of various modifications Within the scope of the appended claims. In the claims, it will be understood that the expressions 3 and 5 position substituted derivatives, and 3, 5 and 6 position substituted derivatives are intended to embrace not only those compounds substituted in all of the named positions, but in any one of the named positions or combinations thereof.

What is claimed is:

1. An aqueous acid bath solution for electroplating nickel containing at least one nickel salt as a source of nickel, which plating solution includes an organic compound selected from the group consisting of the diketo and imino keto thiazolidines and selenazolidines, and the 3 and 5 position substituted derivatives thereof; and the diketo and imino keto thiazines and selenazines, and the 3, 5 and 6 substituted derivatives thereof; said solution having a pH of not less than 2.5 and not exceeding about 5.0; said compound being dissolved in the bath solution in sufiicient quantity to effect leveling and brightening of nickel deposits produced therein.

2. A nickel plating solution as defined in claim 1, wherein the amount of said organic compound ranges from about 0.01 to 1.0 gram per liter of solution.

3. A nickel plating solution as defined in claim 2,

wherein said organic compound is selected from the group consisting of 2,4-diketo thiazolidine and the 3 and S substituted derivatives thereof, said compound being present in the solution in amounts of from about 0.01 to 0.10 gram per liter.

4. A nickel plating bath as defined in claim 2, wherein said organic compound is selected from the group consisting of 2-imino 4-keto thiazolidine and the 3 and S substituted derivatives thereof, said compound being present in the solution in amounts of from about 0.05 to 1.0 gram per liter.

5. A nickel plating solution as defined in claim 1, which furtherincludes a primary brightening agent selected from the group consisting of the naphthalene, naphthol, naphthylamine, toluidine and tolidine sulfonic acids and mildly chlorinated derivatives of these; and the aryl sulfonamides and sulfimides; the amount of such primary brightening agent ranging from about 0.5 to 25.0 grams per liter of solution.

6. A nickel plating solution as defined in claim 5, wherein there is also present an organic compound serving to extend the low limit of operable cathode current density of such a plating solution, said extender comprising a nonionic surfactant material, the amount of such extender in solution ranging from about 0.005 to 0.10 gram per liter, said extender having a molecular weight on the order of at least 7000.

7. A nickel plating solution as defined in claim 5, wherein there is also present an organic compound serving to extend the low limit of operable cathode current density of such a plating solution, said extender comprising an amino compound selected from the group consisting of ethylenediamine tetraacetonitrile, adenine sulfate, tetraethylene pentamine and methyl violet, said extender being present in solution in amounts of from 0.01 to not exceeding about 0.10 gram per liter.

8. A nickel plating solution as defined in claim 5, wherein there is also present an organic compound serving to extend the low limit of operable cathode current density of such a plating solution, said extender comprising a member selected from the group consisting of nucleic acid, Carbowax 20M and terephthalonitrile; said extender being present in solution in amounts of from 0.01 to not exceeding about 0.05 gram per liter.

9. A nickel plating solution as defined in claim 5, wherein there is also present a small amount of an amino polyaryl methane serving as a secondary brightening agent and selected from the group consisting of fuchsin, reduced fuchsin, p,p-methylene dianiline and 2,2',4,4-tetramino-5,5-dimethyl diphenylmethane; the amount of such secondary brightening agent in solution ranging from about 2 to 100 milligrams per liter.

10. An aqueous acid bath solution for nickel plating containing at least one nickel salt as a source of the nickel, which plating solution includes up to 1.0 gram per liter of an organic compound sufficient to improve the leveling action of said plating solution, said compound being selected from the class consisting of the 5 and 6 membered heterocyclic compounds having the following structural formulae:

ll 0:\-TH NH \M/:X M/LX and the 3 and 5, and 3, 5 and 6 substituted derivatives, respectively, thereof, wherein the substitutions at said positions consist of radicals selected from the group consisting of: nitro; halo; sulfo; amino; carboxy; hydroxy; aldehyde; oxy; alkyl, alkene and alkyne radicals containing up to 6 carbons, and the amino, nitro, halo, sulfo, carboxy, hydroxy, aldehyde and oxy derivatives of said alkyl, alkene and alkyne radicals; and phenyl and benzyl radicals, and the nitro, halo, sulfo, amino, carboxy, hydroxy and oxy derivatives of said phenyl and benzyl radicals; wherein M represents a member selected from the group consisting of sulfur and selenium; and wherein X represents a member selected from the group consisting of oxy and imino radicals; said bath having a pH of not less than 2.5 and not exceeding about 5.0.

11. An electroplating bath for producing a bright nickel deposit of improved leveling properties, comprising an aqueous acid solution which, in addition to water, consists essentially of a predominating amount of an inorganic nickel salt providing the equivalent of from about 40 to 120 grams per liter of nickel in solution, from about 8 to 50 grams per liter of boric acid, from about 0.5 to 25.0 grams per liter of a naphthalene sulfonic acid, from about 2 to 100 milligrams per liter of reduced fuchsin, approximately 0.1 gram per liter of sodium lauryl sulfate, and from about 0.02 to 0.10 gram per liter of a leveling agent selected from the group consisting of 2,4-diketo thiazolidine and the 3 and 5 position substituted derivatives thereof wherein the radicals of the substituent groups are selected from the group consisting of: nitro; halo; sulfo; amino; carboxy; hydroxy, aldehyde; oxy; alkyl, alkene and alkyne radicals containing up to 6 carbons and the amino, nitro, halo, sulfo, carboxy, hydroxy and oxy derivatives of said alkyl, alkene and alkyne radicals; and phenyl and benzyl radicals and the nitro, halo, sulfo, amino, carboxy, hydroxy and oxy derivatives of said phenyl and benzyl radicals.

12. An electroplating bath for producing a nickel deposit as defined in claim 11, which further includes an organic extender agent for improving the operation of said bath at low cathode current densities, said extender agent comprising about 0.005 to 0.10 gram per liter of an organic nonionic surfactant compound having a molecular weight on the order of at least 7,000 and resulting from the reaction of propylene glycol and ethylene oxide.

13. An electroplating bath for producing a bright nickel deposit of improved leveling properties, which comprises, per liter of solution:

' Grams Nickel sulfate, approx. 300 Nickel chloride, aprox. 60 Boric acid, approx. 45 Sodium lauryl sulfate, approx. 0.12

in combination with from 0.01 to 0.10 gram per liter of 2,4-diketo thiazolidine as a leveling and brightening agent.

14. An electroplating bath as defined in claim 13, wherein said bath further includes about 0.01 to 0.10 gram per liter of the reaction product of propylene glycol and ethylene oxide having a molecular weight of about 7000.

15. An electroplating bath as defined in claim 14, which further includes approximately 5.0 grams per liter of naphthalene 'disulfonic acid.

16. The process of producing nickel deposits of improved leveling characteristics on a basis metal, which comprises electrodepositing nickel from an aqueous acid bath containing the nickel mainly in the form of a soluble inorganic salt, in the presence of from about 0.01 to not exceeding 1.0 gram per liter of solution of an organic leveling agent selected from the group consisting of the diketo and imino keto thiazolidines and selenazolidines, and the 3 and 5 position substituted derivatives thereof; and the diketo and imino keto thiazines and selenazines, and the 3, 5 and 6 substituted derivatives thereof; the pH of said bath being not less than 2.5 and not substantially exceeding 5 .0, the temperature being on the order of 30 to C. and the cathode current density being on the order of at least 30 amperes per square foot.

17. The process of producing nickel deposits as defined in claim 16, wherein said oath further includes an amount of from 0.5 to 25.0 grams per liter of a primary brightener selected from the group consisting of the naphthylene, naphthol, naphthylarnine, toluidine and tolidine sulfonic acids and mildly chlorinated derivatives of these, and the aryl sulfonamides and sulfimides; the cathode current density being on the order of at least 20 amperes per square foot.

18. The process of producing nickel deposits as defined in claim 17, wherein said bath further includes from 0.005 to 0.10 gram per liter of an organic nonionic surfactant material, having a molecular weight of at least about 7,000, wherein the cathode current density is on the order of at least 10 amperes per square foot.

19. The process of producing nickel deposits as defined in claim 17 wherein said bath further includes from about 0.01 to not more than 0.10 gram per liter of an organic extender comprising an amino compound selected from the group consisting of ethylenediamine tetraacetonitrile, adenine sulfate, tetraethylene pentamine and .methyl violet, and wherein the cathode current density is on the order of at least 10 amperes per square foot.

20. The process of producingnickel deposits as defined in claim 17, wherein said bath also includes an organic extender comprising a member selected from the group consisting of nucleic acid, Carbowax -M and terephthalonitrile in amount of from about 0.01 to not more than about 0.05 gram per liter, wherein the cathode current density is on the order of at least 10 amperes per square foot.

21. The process of producing nickel deposits as defined in claim 17, wherein said bath also includes from about 2 to 100 milligrams per liter of a secondary brightening agent selected from the group consisting of fuchsin, reduced fuchsin, p,p-methylene dianiline and 2,2',4,4- tetramino-5,5-dimethyl diphenylmethane.

22. The process of producing nickel deposits of improved leveling characteristics on a basis metal, which comprises electrodepositing nickel in an aqueous acid solution containing, in addition to water, a preponderating amount of an inorganic nickel salt providing the equivalent of from about 40 to 120 grams per liter of nickel in solution, from about 8 to 50 grams per liter of boric acid, from about 0.5 to 25.0 grams per liter of a naphthalene sulfonic acid, from about 2 to 100 milligrams per liter of a member selected from the group consisting of fuchsin and reduced fuchsin, approximately 0.10 gram per liter of sodium lauryl sulfate, and from about 0.02 to 0.10 gram per liter of a leveling agent selected from the group consisting of 2,4-diketo thiazolidine and the 3 and 5 position substituted derivatives thereof wherein the radicals of the substituent groups are selected from the group consisting of: nitro; halo; sulfo; amino; carboxy; hydroxy; aldehyde; oxy; alkyl, alkene and alkyne radicals containing up to 6 carbons and the amino, nitro, halo, sulfo, carboxy, hydroxy, aldehyde and oxy derivatives of said alkyl, alkene and alkyne radicals; and phenyl and benzyl radicals, and the nitro, halo, sulfo, amino, carboxy, hydroxy, aldehyde and oxy derivatives 16 of said phenyl and benzyl radicals; the pH of said bath being not less than 2.5 and not substantially more than 5.0, the temperature being about 30 to 80 C., and the cathode current density being on the order of about 20 amperes per square foot.

23. The process of producing nickel deposits as defined in claim 22, wherein said bath solution also contains from about 0.005 to 0.10 gram per liter of an organic non-ionic surfactant material having a molecular weight on the order of at least 7,000; and the cathode current density is on the order of at least 10 amperes per square foot.

24. The process of producing bright nickel deposits of improved leveling characteristics on a basis metal,

which comprises electroplating nickel from an acid bath containing, per liter of solution:

Grams Nickel sulfate, approx 300 Nickel chloride, approx. 60 Boric acid, approx. Sodium lauryl sulfate, approx. 0.12

in combination with from 0.01 to 0.10 gram per liter of 2,4-diketo thiazolidine; the temperature of the bath be ing about C. and the pH being about 3.0, with a cathode current density of around 30 amperes per square foot.

25. The process as defined in claim 24, wherein said bath further includes approximately 5.0 to 8.0 grams per liter of naphthalene disulfonic acid.

26. The process as defined in claim 25, wherein said bath further includes at least 0.002 but not more than 0.02 gram per liter of reduced fuchsin.

References Cited in the file of this patent UNITED STATES PATENTS 2,837,472 Gundel et al June 3, 1958 2,849,351 Gundel et al Aug. 26, 1958 2,872,392 Martin Feb. 3, 1959 2,892,760 Gundel et al June 30, 1959 

1. AN AQUEOUS ACID BATH SOLUTION FRO ELECTROPLATING NICKEL CONTAINING AT LEAST ONE NICKEL SALT AS A SOURCE OF NICKEL, WHICH PLATING SOLUTION INCLUDEDS AS ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE DIKETO AND IMINO KETO THIAZOLIDINES AND SELENAZOLIDINES, AND THE 3 AND 5 POSITION SUBSTITUTED DERIVATIVES THEREOF; AND THE DIKETO AND IMINO KETO THIAZINES AND SELENAZINES, AND THE 3, 5 AND 6 SUBSTITUTED DERIVATIVES THEREAFTER; SAID SOLUTION HAVING A PH OF NOT LESS THAN 2.5 AND NOT EXCEEDING ABOUT 5.0; SAID COMPOUND BEING DISSOLVED IN THE BATH SOLUTION IN SUFFICIENT QUANTITY TO EFFECT LEVELING AND BRIGHTENING OF NICKEL DEPOSITS PRODUCED THEREIN. 